Side shift clamp device

ABSTRACT

A hydraulically operated side shift clamping device for use in a fork lift or light cargo conveying appliance. The device comprises two hydraulically operated cylinders having pistons which pistons operate to open and close clamping arms attached thereto. A first oil passage supplies oil commonly to the space in the hydraulic cylinder rearwardly of the pistons while second and third oil passages are connected respectively to each hydraulic cylinder forwardly of the pistons. A short circuit connection is provided between the second and third oil passages which short circuit connection has a pair of oppositely arranged pilot check valves. A further pilot check valve is provided in the first oil passageway and a pilot connection is made between the intermediate point of connection of the two pilot check valves short circuiting the second and third oil passages and the pilot check valve in the first oil passageway.

ite States Patent 1191 Kawanishi et a1.

[11] 3,831,795 Aug. 27, 1974 SllDE SHIFT CLAMP DEVICE [73] Assignee: Kabushiki Kaisha Toyoda Tidoshokki Seisakusho, Kariya-shi, Japan [22] Filed: July 12, 1972 [21] Appl. No.: 271,200

[30] Foreign Application Priority Data July l3, l97l Japan 46-51998 July 28, 1971 Japan 46-56659 52 us. ca. 214/731 511 1m. (:1 B66f9/141 58 new 01 Search 214/651, 653, 654, 655, 214/730, 731

[56] References Cited UNITED STATES PATENTS 3,166,207 1/1965 Quayle 2l4/653 3,692,l98 9/1972 Lake 2l4/653 Primary Examiner-Robert G. Sheridan Assistant Examiner-Lawrence J. Oresky Attorney, Agent, or FirmI-lolman & Stern ABSTRACT A hydraulically operated side shift clamping device for use in a fork lift or light cargo conveying appliance. The device comprises two hydraulically operated cylinders having pistons which pistons operate to open and close clamping arms attached thereto. A first oil passage supplies oil commonly to the space in the hydraulic cylinder rearwardly of the pistons while second and third oil passages are connected respectively to each hydraulic cylinder forwardly of the pistons. A short circuit connection is provided between the second and third oil passages which short circuit connec tion has a pair of oppositely arranged pilot check valves. A further pilot check valve is provided in the first oil passageway and a pilot connection is made between the interrnediate point of connection of the two pilot check valves short circuiting the second and third oil passages and the pilot check valve in the first oil passageway.

7 Claims, 6 Drawing Figures PAIENTED Alli 2271974 101 b 1026 F G. 3

MENIEDMIBETW 383L795 mm M is FIG 4 102 102' 7* R 102m 102C 1025 H 13a ,v [Y

SIDE SHIFT CLAMP DEVICE BACKGROUND OF THE INVENTION This invention relates generally to improvements in and relating to a fork lift or the like cargo conveying appliances. More specifically to an improved side shift clamping device adapted for use on the said kind of cargo-handling appliances, especially suitable in use in a highly crowded and space limited working place, as in a ware house, factory or the like, for conveniently shifting a once clamped cargo or load.

The aforementioned kind of side shift clamping device is mostly used in the form of an attachement to the fork lift and comprises a control valve means fixedly mounted on the chassis of the fork lift, and a cargohandling means including hydraulic cylinders and arranged movable on and along the mast member of the fork lift. For hydraulic connection between the control valve means and the cargo-handling means, three or four hydraulic conduit tubings, preferably rubber hoses are used. In the former type of hydraulic connection, it is rather convenient to provide a unlimited front viewing field to the operator of the fork lift and a rather simplified piping job in the manufacture thereof. On the other hand, however, the former type hydraulic connection system, one of the three hoses which is connected to the outer hydraulic chambers of a pair of opposedly arranged cargo clamp piston-cylinder assemblies may frequently be subjected to a high oil pressure as caused to generate by the reaction by or its own weight of the clamped and shifting cargo, and thus, the practically connecting and movable portion of the hose extending between the chassis side part and the cargohandling side part is subjected to severe and repeated bending stresses and during preserving therein a high hydraulic pressure and may be broken which results in a grave drawback and loss of safety and reliance.

On the other hand, in the case of the latter type of hydraulic connection, it is highly convenient that all the connection hoses are kept at a low hydraulic pressure level even at the cargo clamping period, thus providing better reliability and safety. On the other hand, only a worsened front viewing capability is provided to the operator. A rather complicated piping job must be performed during the manufacture of the fork lift.

SUMMARY OF THE INVENTION The main object of the invention is to provide a hydraulically operated cargo side shift and clamping arrangement having the superior qualities which are present in both kinds of conventional appliances, yet capable of removing their inherent conventional drawbacks to a substantial degree.

BRIEF DESCRIPTION OF THE DRAWINGS These and further objects, and features of the present invention will become more apparent when read the following detailed description of the invention by reference to the accompanying drawings in which:

FIG. I is a schematic connection diagram of a preferred first embodiment of the invention.

FIG. 2 is a similar view to FIG. 1, showing a preferred second embodiment of the invention.

FIG. 3 is an enlarged sectional view of a control valve assembly employed in the second embodiment of the invention.

FIG. 4 is a more specific connection diagram of the second embodiment.

FIG. 5 is a side view of a fork lift fitted with the first embodiment.

FIG. 6 is an end view of the fork lift.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. I, numeral 1 represents a first flexible conduit tubing, preferably a rubber hose which is hydraulically connected through branch hoses Ia and la to the outer chambers of separated hydraulic cylinders 2 and 2', respectively. These outer cylinder chambers are denoted 2b and 2b, respectively.

In the interior spaces of these hydraulic cylinders 2 and 2, pistons 2c and 2c are slidably mounted, and piston rods 2a and 2a are attached rigidly at their inner ends to these pistons, respectively. These piston rods 2a and 2a protrude sealingly from inside through sealed guide openings, not shown formed through the respective outer end walls of the hydraulic cylinders 2 and 2' to outside thereof, although the related parts have been shown in a highly schematic way. The first hose 1 includes at its intermediate point near the cylinders a pilot check valve 3, only schematically shown, and is connected further to a changeover valve P, not shown in detail but well-known in the art, mounted on the chassis of a powered vehicle.

Numerals 4 and 5 represent second and third flexible conduit tubings, preferably rubber hoses, the upper ends of these hoses being connected with respective inner chambers 2d and 2d of the cylinders 2 and 2, as shown. The lower parts of these hoses 4 and 5 are jointly connected with a sixth flexible conduit tubing 25, preferably rubber hose, which is connected to the aforesaid change-over valve assembly, not shown, serving for the clamping service, as will be more fully described hereinafter.

Near the said common junction with the hose 25, the second and third hoses 4 and 5 are provided respectively with pilot check valves 6 and 7 which are shown also in a highly simplified way.

Near the hydraulic cylinder 2, the second hose 4 is provided with a flow control valve 8 and a pilot check valve 10, shown only schematically, arranged in paral' lel with each other. In a similar way, the third hose 5 is provided in proximity to the hydraulic cylinder 2 with a flow control valve 9 and a pilot check valve 11, only schematically shown, arranged in parallel to each other.

A connecting hose 12 connects at the loading and unloading service side, referred to only as the service side hereinafter, between the second and third hoses 4 and S and includes therein a pair of oppositely arranged pilot check valves 13 and 14.

Numeral 15 represents a pilot line connecting an intermediate point of the hose 12 between pilot check valves 13 and 14, with the check valve 3 in the hose 1.

Numeral 16 represents a further pilot line connecting the second hose 4 with the pilot check valve 11 in the third hose 5 at the service side, a branch pilot line 17 being connected between an intermediate point of pilot line 16 and the pilot check valve 14 in the connecting hose 12.

A further pilot line 18 connects the third hose 5 and the pilot check valve 10 provided at the service side and in the second hose 4 in its broadened sense. A branch pilot line 19 connects the line 18 with the pilot check valve 13 in the connecting hose 12.

A still further pilot line 20 is connected between pilot check valves 6 and 7.

These pilot lines are shown in dotted lines for better identification only.

A fourth hose 21 connects the second hose 4 with a change-over valve Q, not shown in detail but wellknown in the art, provided at the chassis side for the side shift service.

A fifth hose 22 connects the third hose 5 with the same change-over valve adapted for side shift service.

The operation of the aforementioned system is as follows:

CLAMPING OPERATION In this case, pressure oil is delivered from a feed pump, not shown, upon manipulation of the changeover valve for the clamping service, to the first hose 1, thence through its pilot check valve 3 and branch hoses la and la to the outer or piston rod side chambers 2b and 2b of the hydraulic cylinders 2 and 2, respectively, thereby the pistons 20 and 20, together with their respective piston rods 2a and 2a are moved inwardly in opposite directions, while, at the same time, excess oil is forced out from the inner chambers 20! and 2d of the cylinders to the second and third hoses 4 and 5, respectively. This return oil will be conveyed through pilot check valves and M and main parts of these hoses to pilot check valves 6 and 7 where it is checked off provisionally, A part of this return oil will pass naturally through the flow control valves 8 and 9.

Since the pilot line is connected hydraulically with the first hose 1, pilot check valves 6 and 7 will be released to open upon increase of the oil pressure in pilot line 20. When this check valve release occurs, the re turn oil will be discharged from the hoses 4i and 5 into the sixth hose which leads to a return oil reservoir, not shown.

With inward movement of the piston rod assemblies 20; 2a and 2c';2a, clamp arms 2323 rigidly attached to the respective rods 2a and 2a are also moved inwardly in unison with the hydraulic pistons 2c;2c, respectively so that a load, only schematically shown at 24, will be clamped by and between these arms. In this case, the fourth and fifth hoses 21 and 22 are hydraulically interrupted from the pressure oil supply pump and the like by proper manipulation of the side shift service change-over valve. Therefore, these pipes have nothing to do with the related oil supply and discharge services at this stage.

CLAMP RELEASE OPERATION In this case, a small amount of pressure oil is introduced from the sixth hose 25 into the second and third hoses 4 and 5, thence through pilot check valves 6;7 and flow control valves 8;9 to the inner hydraulic chambers 2d and 2d of the cylinders 2 and 2', respectively. At the same time, excess oil is discharged from the outer chambers 2b;2b of the hydraulic cylinder through respective branch hoses lla;la into the first hose I and provisionally checked off at 3.

With increase of the oil pressure in the second and third hoses 4;5, the oil pressure prevailing in pilot lines 16;l7 and 1.8;19 will be increased to such a degree that pilot check valves 11;]14 and l0;13 are caused hydraulically to open for allowing oil passage therethrough. In this way, the connecting hose 12 becomes conductive and the oil pressure in pilot line 15 will become increased to such degree that the pilot check valve 3 is opened hydraulically thereby. Thus, pressure oil will flow from the hoses 4-;5 through pilot check valves l0;lll to the inner cylinder chambers 2d;2d while return oil will be conveyed to flow from hose 1 through pilot check valve 3, thence being discharged. Therefore, the respective hydraulic pistons 2c,'2c, together with piston rods 2a;2a and clamp arms 2323, are caused to move hydraulically outerwards. Thus, the foregoing clamped condition of the load 24 will become released.

Also, in this case, the fourth and fifth hoses 2ll;22 are hydraulically isolated by manipulation of the side shift valve means and thus, having nothing to do with the related pressure oil supply and return oil discharge.

RIGHTWARD SIDE SHIFT OPERATION In this case, pressure oil is delivered from the fifth hose 22 by manipulation of the side shift service changeover valve means, to the third hose 5. The oil is conveyed therealong through flow control valve 9 to the inner hydraulic chamber 211 of the cylinder 2', while excess oil is discharged from the outer hydraulic chamber 2b of the same cylinder, and introduced through branch hoses Ia;la to the outer chamber 2b of the opposite cylinder 2. At the same time, excess oil will be discharged from the inner chamber 2d of cylinder 2, mainly through pilot check valve 10, thence through the hoses 4 and 21. Therefore, the pistons 20,20 move to the right as viewed in FIG. 1 together with respective piston rods 2a;2a and clamp arms 23;23.

In this case, the pressure oil delivered from fifth and third hoses 22 and 5 passes solely through the flow control valve 9 to the inner chamber 2d of the cylinder 2, while the return oil discharged from the inner chamber 2d of the other cylinder 2 is passed solely through the pilot check valve 10. Therefore, the oil pressure prevailing in the third hose 5 having a relative high flow resistance will become higher than that prevailing in the second hose 4. Thus, the pilot check valves M13 subjected to the influence of the oil pressure prevailing in the pilot lines I8;19 will be caused hydraulically to open, while those denoted with 111;]14 subjected to oil pressure in the pilot lines 116;I7 kept in communication with the second hose, and that denoted with which is provided in the first hose 1 are not opened.

It will be seen, therefore, that the pressure differential between the oil inlet side and the oil delivery side is caused to be stabilized so as to perform an optimum operation intended in this case. In addition thereto, a gentle side shift operation can be assured with use of the aforementioned system, resulting in an easy handling of the load.

It will be further seen that the opposite or leftward shift operation can be carried out in the opposite way in the case of the above system. For understanding of the foregoing embodiment of the invention, no further analysis is necessary, and thus, can be omitted.

In the above-mentioned rightward or leftward shift operation, the first and sixth hoses are isolated from the source and they have nothing to do with the oil feed and discharge.

It will be appreciated therefore that, when expressed in the broadened sense, there is provided in the foregoing first embodiment, a first oil passage route, as em bodied by the first hose, which connects hydraulically the piston rod side chambers of an oppositely arranged pair of hydraulic piston-cylinder assemblies with each other and includes a sole clamp service change-over valve, and second and third oil passage routes, as embodied by the second and third hoses, which are connected hydraulically and respectively with the respective inner hydraulic chambers of the cylinders of said assemblies, each of these routes being provided with a clamp service change-over valve and a side shift service change-over valve in a respective parallel connection mode. In this system, a connecting oil passage route, as embodied by a hose, is provided for hydraulic connection between the second and third oil passage routes, said connecting route being fitted with a pair of oppositely arranged pilot check valves which are hydrauli cally connected through respective pilot lines with the second and third oil passage routes, respectively. in addition, the pilot check valve provided in the first oil passage route is hydraulically connected with the connecting route by means of a further pilot line.

it will thus be seen that in the case of the above first embodiment, only three oil passage routes, more specifically, the first to third oil passage routes can be used for performing the necessary lateral shift jobs, in place of the conventional arrangement of at least four oil passage routes for performing the same purpose. By use of the presently improved arrangement, the driver of a fork lift enjoys substantially improved front viewing possibilities. in addition, the piping job can be substantially simplified and economized. Further, the oil pressure prevailing in the oil passage routes during the load clamping period can be kept at a rather lower level, thus resulting in the reduction of oil leakage and in the corresponding elongation of durable life of the hydraulic system.

Next, referring to FIG. l, a second embodiment of the invention will be described in detail hereinbelow.

In the present embodiment, a pair of opposedly ar ranged hydraulic cylinders T02 and R02 are provided, as before. Numerals l;l0lla;lltlla;i02a;lll2a;ll02b;]lll2b';l2c;M20; i2d;12d;l03;ltl4;l05;ll23;l23' and 124 correspond in their arrangement and function substantially to those denoted l;la;]la;2a;- 2a';2b;2b';2c;2c;2d;2d';3;4;5;23;23 and 24, respectively.

The first hose 101 leads to a clamp service changeover valve 26 provided in a control unit A which is fixedly mounted on the chassis of the fork lift.

Branch hoses 104a and ltMb are branched off from the second and third hoses 104 and 105, respectively, and lead to a side shift service change-over valve 27. Further branch hoses lMb and WSb are branched off from the hoses 1M and 105, respectively, and lead to clamp service change-over valve 26.

A supply pipe means 29, containing an oil supply pump 28, leads to the both change-over valves 26 and 27. This pipe means 29 comprises a branch pipe 29a which leads to the side shift service change-over valve 27, and a further branch pipe 29b which leads to the clamp service change-over valve 28 and contains a check valve 130. The provision of this check valve 130 serves for prevention of a reverse oil flow from the piston rod side hydraulic chambers i021) and 1021) of the cylinders 102 and 1 .02, respectively.

An unloading pipe 290 branched off from the supply pipe 29 passes through the both change-over valves 26 and 27 one after another and is connected with a discharge pipe 32 which leads to a discharge basin 30.

A relief valve 31 is provided, so as to short-circuit of the supply pipe 29 to the discharge basin 30. The purpose of this provision is such that an occasionally developed high oil pressure in the supply pipe 29 at the arrival of the hydraulic pistons 1102c and 102C at their stroke ends may be safely released to the basin 30.

Branches 32a and 32b are branched off from the discharge pipe 32 and connected to the change-over valves 27 and 26, respectively.

Within the territory of the change-over valve 26 adapted for the lead-clamp service, a connection pipe 33 is provided. This pipe 33 serves, by cooperation with the valve 26, for simultaneous connection of branch hoses lltMlb and ltlSb therewith, or, separate connection of supply branch pipe 2% or discharge branch pipe 32b therewith.

A pilot line means 115 is provided for on-off control of said pilot check valve 103. This pilot line means 115 comprises three branch lines, although not specifically denoted for avoidance of confusion of the drawing, which are fitted with respective flow limiting passage means providing a throttling effect and kept in fluid connection with said first, second and third hoses 101, 104 and 105, respectively. Practical details thereof are shown by way of example in FIG. 3.

In FIG. 3, there are provided two threaded sockets W4C and W5C which are kept in fluid connection with said second and third hoses MM and through branch pipe means, respectively, although not specifically shown. Numeral lltllb represents threaded sockets kept in fluid communication with the first hose llfill, although not specifically shown.

The pilot check valve 103 is also seen in this figure which valve is urged to move rightwards in its closing direction by means of a back-up spring 103a, so as to cut off normally the first hose.

There is provided a balance piston 1 ,37 which is urged hydraulically to move leftwards in FIG. 3 under the influence of the oil pressure prevailing in the pilot line H5 and introduced into the interior space of the valve containing movably the balance piston, through the pipe-receiving sockets ltMl-c and 105C and the flow restricting means or throttles 35 and 36, respectively. When the thus hydraulically developed axial thrust acting upon the balance piston T37 exceeds the resilient urging force provided by the back-up spring W311, the hydraulic circuit including the first hose 101 is caused to open.

The opposite end surfaces of the balance piston 137 are acted upon by the respective hydraulic pressures prevailing in the first hose lllll and the pilot line 1115. it should be noted that the first hose and the pilot line are kept in fluid connection by means of flow-reducing passage 34 which extends longitudinally through the body of the balance piston. Check. valves 37 and 38 are provided, as seen, for allowing pressure oil discharge from the said pilot line to the sockets mac and i050 communicating with the second and third hoses, respectively.

The operation of the second embodiment is as follows:

With both change-over valve assemblies 26 and 27 kept in their neutral position as shown, the first hose 101, the supply branch pipes 29a;29b and the respective branch pipes 104:1;104lb and 105a;105b of second and third hoses 104 and 105 are fluidically isolated from each other through the action of the change-over valve assemblies 26;27. Thus, the hydraulic pistons 102C and 102C in the cylinders 102 and 102' are kept stationary.

Pressure oil delivered from pump 28 will be returned through supply branch pipe 290 to the return oil basin 30 Under the influence of the weight of a treating body or the action of the load 124, the hydraulic pistons 102C and 1020 may be urged mechanically to expand from each other. In practice, however, such reactive and expanding movement of these hydraulic pistons may be positively prevented in a hydraulic way, since a discharge of excess oil from the piston rod side chambers 102b and 102b is checked from its occurence, indeed, by virtue of the provision of the pilot check valve 103. It should be noted further that no pressure oil is supplied to the second and third hoses 104 and 105, the balance piston 137 being not acted upon by a substantial hydraulic pressure for exceeding the urging spring pressure at 103a. Therefore, it may well be seen that the first, second and third hoses 1111;104 and 105 in the present embodiment, which connect the control valve device A fixed on the chassis with the cargo handling device B including said hydraulic cylinders 102 and 102 and vertically shiftable, can been maintained at a rather lower hydraulic pressure even with the load or cargo 124 clamped in position. When the device B is moved up-and-down as desired under these operating conditions, these hoses 101;]04 and 105 may be subjected to flexture in an easy way and the fear of breakage of these hoses can be reduced to a possible mini mum.

The operation of the second embodiment with actuation of hydraulic cylinders 102 and 102 by manipulation of change-over valve means 26 and 27 may be explained in the following way. This possibility of manual control of these valve means 27 and 27 is hinted in FIG. 2 by the expression of MAN.

CLAMPING OPERATION When shifting the change-over valve means 26 manually in the right-hand direction, fluid communication of supply branch 290 with source is interrupted, while supply branch 2% and first hose 101 are brought into fluid communication with each other. At the same time, the branches 1041b; 105b of second and third hoses 104105, connecting pipe 33 and branch discharge pipe 3212 are brought into fluid communication. Therefore, pressure oil delivered from pump 28 is conveyed through supply pipe 29, supply branch 2% and first hose 101 to pilot check valve 103 which is thus opened forcibly. The pressure oil is thence delivered to the piston rod side chamber 102b;102b of the cylinders 102;102. Therefore, the pistons 1020,1020 are hydraulically contracted with each other, to which movement the clamp arms 23;23 will follow, so as to clamp the load or cargo 124 only schematically represented. At the same time, excess oil is discharged from the inner chambers 102d;102d through second and third hoses 104;105, branches 104b;105b and connection pipe 33, thence through discharge branch 32b to the return basin 30.

CLAMP RELEASE OPERATION When change-over valve means 26 is shifted manually in the left-hand direction in FIG. 2, supply branch 290 is hydraulically interrupted from source, while supply branch 29b and connection pipe 33 are brought into fluid communication. At the same time, the pipe 33 and branches 1041),"b of second and third hoses 104;105 are brought into fluid communication. Thus, pressure oil delivered from pump 28 will be conveyed through supply pipe 29, supply branch 2%, connection pipe 33, and branches 1041;;105b of second and third hoses 1045105 to the inner chambers 102d;102d of the hydraulic cylinders. Therefore, the pistons 102c;102c are operated to expand the mutual distance between clamp arms 123 and 123' for performing a clamp release job. The oil pressure prevailing in the first hose 101 is at a low level by virtue of hydraulic communication thereof with discharge branch 32b, while the oil pressure prevailing in second and third hoses 104,105 is kept at a high level by virtue of supply with high pressure oil. Therefore, balance piston 37 is given a substantial value of leftward axial thrust in FIG. 3 and exceeding the back-up spring pressure at 103a, so as to shift the pilot check valve 103 leftwards in FIG. 3. By this valve shift movement, the first hose circuit is opened, allowing the excess oil to be discharged from the piston rod side chambers 102b,'102b of the hydraulic cylinders.

LEFT SIDE SHIFT OPERATION By manual shift of the change-over valve means 27 in the right-hand direction in FIG. 3, supply branch 290 is hydraulically isolated from source, while supply branch 20a and the branch 10 1a of second hose 10 1 are brought into hydraulic communication. At the same time, the branch 105a of third hose 105 and the discharge branch 32a are brought into fluid communication.

Pressure oil delivered from pump 28 will be conveyed, therefore, through supply pipe 29, supply branch 29a, and branch 104a of second hose 104 to the inner hydraulic chambers 102d;ll02d' of the cylinders 102;102. At the same time, excess oil will be conveyed from the piston rod side chamber 1112b of the cylinder 102 through branch pipes 101a to the inner chamber 102d of the opposite cylinder 102. At the same time, oil is delivered from the piston rod side chamber 102b of the same cylinder 102 through branch pipe 101a to the piston rod side chamber 1112b of the opposite cylinder 102. On the other hand, oil is delivered from the inner chamber 102d of the cylinder 102' will be discharged through branch 105a of third hose 105 and the discharge branch 32a to return oil basin 30. In this way, clamp arms 23;23' are jointly shifted leftwards for transferring the load or cargo towards left. At this stage, first hose 101 has been isolated from supply pump 28 by the aforementioned manipulation of the valve 26. On the other hand, concerning the hydraulic circuit adapted for supply of pressure oil from second hose 1041 through throttle 35, pilot line and throttle 34 to first hose 101, a slight amount of pressure oil passed through throttle 35 will not be conveyed through throttle 34, and indeed, it will be returned through check valve 38 to the reservoir 30 by virtue of such that at this stage, the pilot line 115 is kept in fluid communication through check valve 38, third hose 10S, side shift change-over valve means 27 and discharge pipe 32 to the basin or reservoir 30. Therefore, it will be seen that any substantial and enough hydraulic pressure will be maintained in neither first hose 1011 nor pilot line M5 for inviting a leftward shift movement of the pilot check valve 103 in FIG. 3. Further, by virtue of the presence of a substantial flow resistance in the discharge circuit including check valve 38, branch pipe 105a, change-over valve means 27 and discharge branch 32a, an occasional generation of oil pressure in the pilot line I will not invite a leftward thrust to shift the pilot check valve 103 in the left-hand direction, because at this stage the balanced piston 37 is kept at its belanced position and the hydraulic axial thrust acting upon thereupon will be substantially reduced.

Therefore, pilot check valve 103 will well maintain the hydraulically isolated condition of first hose 1011 so that a disengagement of the cargo being subjected now to the side shift operation from its clamped position on account of oil leakage from the first hose can be effectively prevented. A disadvantageous invitation of application of excessive cargo clamping force upon the cargo now under shifting, as may be caused by occasional introduction of pressure oil from the first hose to the connection pipe 101a can also be prevented effectively and positively.

It is recommendable to select the spring force appearing in either of check valve 37 or 38 to a small value, so as to avoid a generation of substantial hydraulic pressure in the pilot line 115.

The rightward cargo shift operation can be brought about in the opposite sense to the foregoing. This shifting mode can be easily understood by consulting with the foregoing description and without setting forth a further analysis of the operation. The effects attainable with use of this second embodiment are substantially similar to those disclosed in the foregoing in connection with the first embodiment.

FIG. 4 represents a more detailed and specific overall piping arrangement of the foregoing second embodiment from which a better understanding may be had by reference to the reference numerals in consultation with the foregoing description.

In FIGS. 5 and ti, a fork lift is shown only schematically which is fitted with the first embodiment of the invention. However, if the second embodiment be fitted to, the general appearance will not be subjected to any substantial alteration. The control valve assembly shown in FIG. 3 is contained in a box 100 fixedly mounted at the root portion of the mast 95 Naturally,

clamp arms 23 and 23 are slidable on and along this mast. For better hydraulic connection among several working parts, telescopic connections 96-99 are employed.

The embodiments of the invention in which an exclusive property or privilege is claimed are as follows:

1. A hydraulically operated cargo shift clamp arrangement, comprising: a pair of stationary hydraulic cylinders oppositely arranged in relation to each other; a hydraulic piston slidably mounted in each of said cylinders; a cargo clamp arm rigidly connected to each of said hydraulic pistons, each of said pistons dividing the interior space of said cylinders into an inner and an outer hydraulic chamber; a first hose means hydrauli cally and commonly connected with said outer hydraulic chambers; a second hose means connected hydraulically with one of said inner hydraulic chambers of said cylinders; a third hose means hydraulically connected with the other one of said inner hydraulic chambers; a clamp change-over valve means and a side shift change-over valve means connected with said first, second and third hose means; a firstpilot check valve means disposed in said first hose means for controlling a flow of oil discharged from said outer chambers of said cylinders; two series connected flow-reducing means connected between said second and third hose means to form a short circuit path therebetween; a pilot line connecting an intermediate point between said two flow-reducing means with said first pilot check valve; a second pilot check valve means connected in parallel with one of said two series connected flow reducing means, between said intermediate point and a respective one of said second and third hose means; a third pilot check valve means connected in parallel with the other one of said two series connected flow reducing means between said intermediate point and the other respective one of said second and third hose means and disposed so as to be operatively opposed to said second pilot check valve means; a balance piston means dis posed in said pilot line and subjected at both its ends to hydraulic pressure from said pilot line and to that prevailing in said first hose means, respectively, and a further flow-reducing means provided in said balance piston to form a reduced oil flow passageway between said second and third hose means and said first hose means at a point downstream of said first check valve means.

2. A hydraulically operated cargo shift clamp arrangement comprising:

a pair of stationary hydraulic cylinders oppositely disposed in relation to each other;

a hydraulic piston having a piston rod and slidably mounted in each of said cylinders, each of said pistons dividing the interior space of said cylinders into an inner and an outer hydraulic chamber;

a clamp arm rigidly connected to each of said piston rods for clamping cargo therebetween;

a first hose means hydraulically connected to both said outer hydraulic chambers;

a second hose means hydraulically connected to one of said inner chambers of said cylinders;

a third hose means hydraulically connected to the other of said inner hydraulic chambers;

a clamp change-over valve means hydraulically connected to said first, second and third hose means;

a side shift change over valve means hydraulically connected to said second and third hose means;

a first pilot check valve means disposed in said first hose means for controlling a flow of oil discharged from said outer chambers of said cylinders;

a second and third series-connected check valve means connected between said second and third hose means and disposed so as to be operatively opposed to one another; and

a first pilot line hydraulically connecting an intermediate point between said series-connected check valve means to said first pilot check valve means, whereby operator control of only the clamp change over valve and the side shift change over valve permits shifting of the clamp arms to either side of a central position in unison or relative movement between said clamps.

3. An arrangement as claimed in claim 2 wherein a second pilot line hydraulically connects one of said second and third pilot check valve means with that one of said second and third hose means to which the other of said second and third check valve means is connected and a third pilot line hydraulically connects the other one of said second and third pilot check valve means with that one of said second and third hose means to which said one of said second and third check valve means is connected.

4. An arrangement as claimed in claim ll wherein said second and third check valve means are provided with by-pass circuits each said by-pass circuit having a flow reducing means which provides increased resistance to flow of oil therethrough.

5. An arrangement as claimed in claim 4 wherein said pilot line is hydraulically connected through an orifice means to said first hose means downstream of said first pilot check valve means.

6. An arrangement as claimed in claim 1 wherein fourth and fifth check valve means are provided in said second and third hose means respectively said fourth and fifth check valve means having by-pass circuits connected in parallel thereto, each said by-pass circuit containing flow reducing means which provide increased resistance to flow of oil therethrough, said fourth and fifth check valve means being connected through pilot lines to said third and second hose means respectively.

7. An arrangement as claimed in claim 2 wherein fourth and fifth check valve means are provided in said second and third hose means respectively said fourth and fifth check valve means having by-pass circuits connected in parallel thereto, each said by-pass circuit containing flow reducing means which provide increased resistance to flow of oil therethrough, said fourth and fifth check valve means being connected through pilot lines to said third and second hose means respectively.

l= l l 

1. A hydraulically operated cargo shift clamp arrangement, comprising: a pair of stationary hydraulic cylinders oppositely arranged in relation to each other; a hydraulic piston slidably mounted in each of said cylinders; a cargo clamp arm rigidly connected to each of said hydraulic pistons, each of said pistons dividing the interior space of said cylinders into an inner and an outer hydraulic chamber; a first hose means hydraulically and commonly connected with said outer hydraulic chambers; a second hose means connected hydraulically with one of said inner hydraulic chambers of said cylinders; a third hose means hydraulically connected with the other one of said inner hydraulic chambers; a clamp change-over valve means and a side shift change-over valve means connected with said first, second and third hose means; a first pilot check valve means disposed in said first hose means for controlling a flow of oil discharged from said outer chambers of said cylinders; two series-connected flow-reducing means connected between said second and third hose means to form a short circuit path therebetween; a pilot line connecting an intermediate point between said two flow-reducing means with said first pilot check valve; a second pilot check valve means connected in parallel with one of said two series connected flow reducing means, between said intermediate point and a respective one of said second and third hose means; a third pilot check valve means connected in parallel with the other one of said two series connected flow reducing means between said intermediate point and the other respective one of said second and third hose means and disposed so as to be operatively opposed to said second pilot check valve means; a balance piston means disposed in said pilot line and subjected at both its ends to hydraulic pressure from said pilot line and to that prevailing in said first hose means, respectively, and a further flow-reducing means provided in said balance piston to form a reduced oil flow passageway between said second and third hose means and said first hose means at a point downstream of said first check valve means.
 2. A hydraulically operated cargo shift clamp arrangement comprising: a pair of stationary hydraulic cylinders oppositely disposed in relation to each other; a hydraulic piston having a piston rod and slidably mounted in each of said cylinders, each of said pistons dividing the interior space of said cylinders into an inner and an outer hydraulic chamber; a clamp arm rigidly connected to each of said piston rods for clamping cargo therebetween; a first hose means hydraulically connected to both said outer hydraulic chambers; a second hose means hydraulically connected to one of said inner chambers of said cylinders; a third hose means hydraulically connected to the other of said inner hydraulic chambers; a clamp change-over valve means hydraulically connected to said first, second and third hose means; a side shift change over valve means hydraulically connected to said second and third hose means; a first pilot check valve means disposed in said first hose means for controlling a flow of oil discharged from said outer chambers of said cylinders; a second and third series-connected check valve means connected between said second and third hose means and disposed so as to be operatively opposed to one another; and a first pilot line hydraulically connecting an intermediate point between said series-connected check valve means to said first pilot check valve means, whereby operator control of only the clamp change over valve and the side shift change over valve permits shifting of the clamp arms to either side of a central position in unison or relative movement between said clamps.
 3. An arrangement as Claimed in claim 2 wherein a second pilot line hydraulically connects one of said second and third pilot check valve means with that one of said second and third hose means to which the other of said second and third check valve means is connected and a third pilot line hydraulically connects the other one of said second and third pilot check valve means with that one of said second and third hose means to which said one of said second and third check valve means is connected.
 4. An arrangement as claimed in claim 1 wherein said second and third check valve means are provided with by-pass circuits each said by-pass circuit having a flow reducing means which provides increased resistance to flow of oil therethrough.
 5. An arrangement as claimed in claim 4 wherein said pilot line is hydraulically connected through an orifice means to said first hose means downstream of said first pilot check valve means.
 6. An arrangement as claimed in claim 1 wherein fourth and fifth check valve means are provided in said second and third hose means respectively said fourth and fifth check valve means having by-pass circuits connected in parallel thereto, each said by-pass circuit containing flow reducing means which provide increased resistance to flow of oil therethrough, said fourth and fifth check valve means being connected through pilot lines to said third and second hose means respectively.
 7. An arrangement as claimed in claim 2 wherein fourth and fifth check valve means are provided in said second and third hose means respectively said fourth and fifth check valve means having by-pass circuits connected in parallel thereto, each said by-pass circuit containing flow reducing means which provide increased resistance to flow of oil therethrough, said fourth and fifth check valve means being connected through pilot lines to said third and second hose means respectively. 